BK Precision 1601 Instruction Manual

INSTRUCTION MANUAL

FOR

B & K-PRECISION

MODEL 1601

SOLID STATE

REGULATED DC POWER

SUPPLY

DYNASCAN

CORPORATION

6460 West

Cortland

Street

Chicago, Illinois 60635

CONTENTS

Page

SPECIFICATIONS

. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

FEATURES . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

3

INTRODUCTION

.....................................................

4

CONTROLS AND INDICATORS

........................................

4

OPERATING INSTRUCTIONS

.........................................

5

APPLICATIONS

.....................................................

6

General

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Electronic Servicing

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Servicing Battery Operated Equipment

.........................

6

Servicing Vehicular Electronics Equipment

.....................

7

Servicing Plug-In Modules.................................... 9

Using Two Power Supplies For Two Output Voltages............9

Two Power Supplies In Series For O-100 Volt Output . . . . . . . . . . . . 9

Using The Power Supply As A Battery Charger

. . .

. . . . . . ... ........... 10

Other Servicing Applications

.................................

10

Electronics Manufacturing

........................................

10

Electronics Design Engineering

.

....................................

11

Electronics Education

............................................

11

CIRCUIT DESCRIPTION

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12

MAINTENANCE

. . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . ..*.................

14

OUTPUT VOLTAGE

OUTPUT CURRENT

CUMNF&~

LOAD REGULATION

FULLY SOLID STATE

CURRENT LIMITING/
OVERLOAD
PROTECTION

SIMPLIFIED

ZZll&TING

(0-50 VDC

0-2

AMPS

DUAL

METERS

SPECIFICATIONS

O-SO VDC, continuously

var-

iable. Two ranges,

0-25

and

O-50 VDC.
O-2 amperes. Four ranges:

O-SO

mA, 0-0.2A. 0-0.5A,

and

0-2A.
5% to 100% of each current

range.
Maximum 0.1%. typical

0.07%.

LINE REGULATION

RIPPLE
CURRENT DERATING

SIZE
NET WEIGHT

FEATURES

Uses integrated circuits, sil­icon transistors and diodes,
and an SCR. All the advan-

tages of solid state construc­tion are utilized, including:

Dependability-reliability

No warm up time or stab-

ilization delay

Ruggedness

Compact size

Protects load and instrument

against overload.

Curr

ent

limit is fully adjustable from
approximately 2.5 mA to 2
A. The power supply auto­matically shuts down and
the OVERLOAD lamp lights
if the preset current limit is

exceeded. After clearing the

cause of the overload, sim­ply push the set/reset button
to restore normal operation.

Permits setting current limit
without disturbing external

load connections or output

voltage settings: does not

re-

quire

application of short
circuit to output terminals.
Simply

push the set/reset

button and adjust the

cur­rent limit while reading the
setting on the current meter.

Continuously adjustable over

entire range with a single
control; no range switching
required.

Divided into four ranges.
Fully regulated output at all
current levels.

Allows output voltage and

current to be monitored si­multaneously without

switch-

ing

ranges from current to

voltage. Both meters have

overload protection to pre-

vent damage from incorrect
range selection.

FOUR CURRENT

METER RANGES

TWO VOLTMETER
RANGES

STANDBY-DC
ON SWITCH

ON-OFF CONTROL

PILOT LAMP

MECHANICAL
PREREGULATOR

FLOATING OUTPUT

REVERSE POLARITY

PROTECTION

BINDING POSTS

ATTRACTIVE
APPEARANCE

EASY TO OPERATE

Maximum 0.1%. 0.02%

typ-

ical, at output Voltage of

50
VDC and output current of 2
amps

from

105-125

VAC.

5

millivolts peak-to-peak

maximum.

.02 A/°C

above

25°

C am-

bient. (2 A Range only).

14 1/8"

x

3 7/8"

x 10” deep.

11 lbs.

Provides maximum meter

resolution. Selection of me­ter range also selects coarse
current limit setting.

0-25V and

0-5OV

ranges pro-

vide maximum meter resolu­tion. A mechanical stop
prevents the voltage level
control from exceeding

ap-

proximately 25 volts when

the O-25 V range is selected.
Standby mode disconnects

power

supply from load
without disturbing voltage
or current control settings.

On-off switch is combined
with voltage level control to

assure voltage setting of

zero when unit is turned on.
Lights to indicate at a glance

that the unit is turned on.

Power supply’s rectifier in­put voltage increases in pro­gressive steps as output
voltage setting is increased.
Improves efficiency; less
power is converted to heat
at low voltage operation.

Permits referencing the posi­tive or negative output to
any external dc potential or
ground.

Protects against accidental

damage from reverse polar­ity connection to external
power source.

Heavy duty

5-way

binding

posts for positive cmd

nega­tive polarity output and earth
ground.

Modem, functional design.
When more

than

one unit

is

used, units may be stacked.
All controls are

identified
and easy to read. Simplified
operation helps prevent op
erator

mistakes that might

damage equipment.

3

INTRODUCTION

The B & K Precision Model 1601 Regulated DC
Power Supply is a versatile, laboratory quality in­strument which provides regulated dc voltage and
current outputs of 0 to 50 volts and 0 to 2 amperes

respectively. Its high specifications, operating ease,
and special features make it an excellent choice
for most applications requiring a dc power source.
It is especially well suited for powering transis­torized and fully solid state electronic equipment
such as automobile radios and sound systems, bat­tery operated radio receivers, portable radios,
mobile citizen’s band transceivers and Walkie-Talkie

transceivers.

The following list is ‘but a small sample of the

most popular applications for the instrument:

-Service Technicians

-Factory Technicians

-Engineers and
Laboratory
Technicians

-Electronics
Instructors
and Students

CONTROLS AND INDICATORS

Powering equipment or indi­vidual circuits during testing
and trouble-shooting in the
service shop.

Powering complete

equip­ments or individual assem­blies during testing in the

factory.

Powering prototype and ex­perimental circuits and
equipments.

Laboratory exercises in basic
and

advanced electronics.

3

2

1

13

12

11

io

Controls and Indicators

1 current meter

Measures actual output load

4 Push to set

current during normal oper-

CURRENT

ation.

LIMIT or to reset

Indicates current limit value

OVERLOAD

when set/reset button 4 is

button (set/

pushed. reset button)

2 CURRENT

Selects range for current

RANGE switch

meter 1 and coarse setting

of current limit. Full scale

meter

reading

and maxi-

mum current limit of:

0.05A

position

0.2A

position

0.05 ampere

(50

milliamps)

0.5A

position

0.2 ampere

(200

milliamps)

2A position

0.5 ampere

(500

milliamps)

2 amperes

5 OVERLOAD

indicator

(red)

6 POWER indicator Lights continuously while

power supply is turned on.

7 STBY-DCON

switch;
STBY position

l

3 SETCURRENT

LIMIT control

Fine adjustment of current
limit setting. Continuously
adjustable from 5% to 100%
of range which is selected
by CURRENT RANGE switch

2

DC ON position

4

When fully depressed and
held, connects current meter

1

to read the current limit
setting. When pressed and
released, resets overload cir­cuit if it has been tripped.

Lights when current limit has
been exceeded and power

supply output has shut down.

Removes power from output

terminals 9 and 10 and

voltmeter

11 but leaves

power supply activated in a

standby condition.

Applies power to output ter-

minals 9 and

10

and

voltmeter

11

*

c

termina1

Earth and chassis ground
terminal.

9 + terminal

Positive polarity Output ter­minal.

10

-

terminal

Negative polarity output
terminal.

11

voltmeter

Indicates power supply out­put voltage.

12

1.

2.

3.

4.

METER

RANGE
switch
0-5OV

position

Selects full scale range of
50 volts for voltmeter 11

0-25V

position

Selects full scale range of
25 volts for voltmeter

11

OPERATING INSTRUCTIONS

a.

b.

C.
d.

13 LEVEL control

Turn off the power supply before plugging it
into an ac outlet. Turn off by

rotating

the LEVEL

control

13 fully counterclockwise until it

“clicks” off.
Connect the power cord to a 105-125 volt 60 Hz

ac outlet.

WARNING

Use only a polarized

3-wire

outlet. This

assures that the power supply chassis is

connected to a good earth ground and pre­vents danger from electrical shock. If a
2-wire

to

3-wire

adapter must be used, be
sure the ground wire of the adapter is
attached to a good earth ground.

Turn on the power supply by rotating the
LEVEL control 13 slightly clockwise past the
“click”. The POWER indicator 6 will light.

Determine the maximum safe load current for
the device to be powered and set the current
limit for that value as follows:

Set the coarse current limit with the CUR-

RENT RANGE switch 2 . When possible,

select a range that provides the desired cur­rent liiit at a value above 20% of the full

scale

reading.

7

.

Return the “STBYDC ON” switch 7 to the
DC ON position and set the output voltage as
follows:

Push and hold the set/reset button 4 while

making

fine

current limit adjustment with

the SET CURRENT

LIMIT

control 3 for the

desired current limit as read on the current

meter

1 .

a.

Release the set/reset button 4 .

b.

If the maximum safe load current is

un-

known,

start with a low current

lit

setting.
If the setting is too low, the overload circuit
will merely trip when power is applied to
the

load in steps 7 and 8. If so, increase the
current limit setting in small steps until the
overload circuit does not trip during normal
operation.

8. If the load current exceeds the current limit, the
OVERLOAD lamp 5 will light and the power

supply will shut down

.(the

current meter 1

and voltmeter 11 will drop to zero). Restore

;~Iowyw=r supply

to normal operation as

.

.

and prevents LEVEL control

13 from increasing the

voltage above approximately

25 volts.
Turns off power supply at

extreme counterclockwise ro-

tation. Clockwise rotation
turns on power supply and
adjusts output voltage (volt-

age output level is not
changed by the METER
RANGE switch 12 ). Also,
prevents METER RANGE
switch from being set to O-25
V position when LEVEL con­trol is advanced beyond

ap-

proximately 25 volt output.

5.

6.

Set the “STBY-DC ON’ switch 7 to the STBY
position

while

connecting the test leads.

Connect the power supply output to the device
being powered with test leads as follows:

a.

b.

C.

Connect the positive polarity input of the

device being powered to the (+) terminal

9 of the power supply.

Connect the negative polarity input of the
device being powered to the

(-)

terminal

10 of the power supply.

If the positive polarity of the device beiig
powered is also to be ground reference,
jumper the (+) terminal 9 to the

(+ )

ter-

minal 8

.

If the negative polarity of the
device being powered is to be ground ref­erence, jumper the

(-)

terminal 10 to the

(hlterminal

8

.

If neither the positive nor

negative polarity of the device bemg pow-

ered is to be grounded, but the chassis of
the device needs grounding, connect a sep­arate test lead from the chassis of the device
to the ( * 1 terminal8of the power supply.

Set the METER RANGE

switch

12 to the

0-25V

position if the output voltage is to be

set for 25 volts or

less,

or to the

0-50V

posi­tion if the output voltage is to be sat for
more than 25 volts.

Turn LEVEL control 13 clockwise until the

desired output voltage is read on the volt-

meter 11 .

5

a.

b.

To reset the power supply, press and release

the

set/reset

button 4 . If the overload
condition was intermittent, this action will
restore operation.

If the OVERLOAD lamp 5 remains lighted,

use one of the three following

techniques

before resetting the power supply again:

-Reduce the load current.

-Reduce the voltage slightly with the

LEVEL control 13

.

-Increase the current limit slightly with the

SET CURRENT LIMIT control 3

.

If the
normal load current is unknown, this tech­nique may be used; but, if the current limit
was already set for the maximum safe
load current, do not increase the current
limit further.

NOTE:

input which results in a surge current
when power is intially applied. When
powering such equipment, the overload
may activate when the STBY-DC ON switch

is placed in the DC ON position with full

operating voltage previously set. If this

occurs, reduce the voltage setting and

bring it up gradually to allow the capaci-

tors in the equipment to charge; this elim­inates the surge current.

c. If the power supply continues to shut

down
at the correct current limit value, check the
LOAD current to determine the reason for

the overload.

9. To remove power from the load without dii
turbing the voltage or current limiting settings,
merely set the “STBY-DC ON” switch 7 in the

Some equipment has a highly capacitive

STBY position.

APPLICATIONS

GENERAL

This instrument may be used to power a vast
assortment of items in the fields of electronics serv­icing, electronics manufacturing, electronics design

engineering and electronics education. The power
suply output is fully adjustable from

0

to 50 volts,
and 0 to 2 amperes. This flexibility makes it suitable
for most applications requiring a dc power source.

ELECTRONICS SERVICING

The electronics technician uses the power supply

as

the power source for much dc and battery
powered equipment being tested and serviced. It
may also be used as the power source for testing
modules or circuits that are removed from the equip
ment where it normally receives its power.

SERVICING BATTERY OPERATED EQUIPMENT

Most equipment which operates from internal bat­teries can be tested and serviced using this power
supply as its power source. The excellent filtering
characteristics makes the power supply a suitable

substitute for batteries, with the added

advantage

that the effects of

varying

the voltage can be

checked. The following items are among the more

6

POKER SUPPLY

common types that may be powered from this
power supply:
Portable

AM or AM/FM radio receivers

Portable short wave and multi-band radio receivers

Portable paging receivers

Portable monitor receivers
Walkie

Talkie type transceivers
Portable two-way communications transceivers
Portable cassette recorders and players

Portable calculators

Other battery operated electrical or electronic

devices

CAUTION

Observe correct polarity. Some equipment

may not contain reverse polarity protec-

tion, and may be damaged if polarities are

reversed.

When servicing this type of equipment, remove

the batteries and connect test leads from the

(+)

and

(-)

terminals of the power supply to the

(+)

and (-)
power input points of the equipment being serviced
as shown in Figure 1. The earth ground terminal of

EQUIPMENT

BEING SERVICED

t

CURRENT LIMIT

Set VOLTAGE to the

to maximum

input

terminal voltage

value

of

fully

charged batteries.

Figure 1. Typical Power Supply Connections to

Battery Operated Equipment

COMPARTMENT

the power supply is not normally used nor required

in this application.

Using separate test lead colors,

such

as red and black, reduces the chance of acci-

dental

reverse polarity connection. Set the current

limit to the maximum input current specification of

the equipment being serviced. If this figure is un­kn

o

wn, start with a low current limit and increase

the setting in small increments until the overload
circuit in the power supply does not trip when power
is applied to the unit under test. Set the voltage to
the same value that would be present if a full set of
fully charged batteries were installed. Flashlight
cells of all sizes are rated at 1.5 volts ‘each. Other
batteries normally state the voltage on the label,
and

the required operating voltage for the equip

ment being serviced is often stated on a label in

the equipment. For units using more than one bat-

tery, check whether the batteries are connected in

series or parallel. For the parallel connected ar­rangement, set the power supply voltage to that of
a single cell; a higher voltage may damage the
equipment. For the series connected arrangement,
add the voltages of all cells and set the power sup

ply voltage to that sum.

A simplified method of making connections to the
power input points of battery operated equipment
may be to use a “dummy” battery. A dummy bat-

tery sits in the battery compartment and makes

good electrical contacts with the power input points,
but has readily accessible terminals or test leads
for interconnection to the power supply. The body
of the dummy battery may be made from wood or
other nonconductive material. The end caps must
be good electrical conductors which are connected
to terminals or test leads. The unit must fig snugly
in the battery compartment to assure good electrical
contact. An improved version may include a spring

to insure a snug fit.
SERVICING VEHICULAR

ELECTRONICS EQUIPMENT

When servicing electronics equipment for auto.

mobiles. trucks, and other vehicles, the equipment
is normally removed from the vehicle for bench

testing.

This power supply is an excellent dc power

source for bench testing such equipment. The

fol-

lowing items are among the more common types of
vehicular electronics equipment that may be
powered from this power supply:

POWER

SUPPLY

AM, AM/FM and AM/FM/Stereo automobile
receivers

*Tape players

Citizen’s band transceivers
Monitor receivers

Automobile amateur radio receivers
*Some aircraft equipment
*Some ship-to-shore and ship-to-ship marine band

transceivers

*Some vehicular two-way communications trans-

ceivers

*Some automotive amateur radio transceivers

‘Maximum current 2 amperes unless special procedures are

used as described in this section of the

manual.

Most automobiles and other vehicles use

12-volt
electrical systems. Although the electrical system is
normally referred to as a

12-volt

system, actual bat-

tery voltage when fully charged is approximately

14 volts. The power supply may be set

at

14 volts

for servicing equipment from vehicles with

12-volt
electrical systems.

Some trucks use a 24-volt

elec-

trical

system; bench testing of equipment from these
systems should be performed at 28 volts. Aircraft
normally use a 28-volt electrical system, and a
bench test voltaqe of 32 volts is used.

Practically all vehicles use a negative ground
electrical system, althouqh a positive ground system
is occasionally found. Electronic equipment which
is built for use only in negative ground vehicles
usually has its chassis common with the negative
polarity of input power. In some cases, there is no
separate negative polarity power cable, since the
chassis

becomes

grounded

when the equipment is
installed in the vehicle. Some equipment is built for
use in either neqative or positive ground electrical
systems, in which case the chassis may be isolated
from both the positive and ‘negative input polarities.
There is virtually no equipment built for positive
ground electrical systems only, although some elec-

tronics equipment may use its ungrounded positive
polarity as reference for circuit operation.

CAUTION
Carefully observe polarity of connections.
Equipment may be damaged if polarities
are reversed.

When servicing this type of equipment, the

(+)

and

(-)

terminals of the power supply should be

connected to the

(+)

and

(-)

power input points of

the equipment being serviced with test leads.

Fig-

EQUIPMENT BEING

SERVICED

to

maximum

input

current

specifi-

cation of

eguipme

being

serviced

+5

Figure 2. Typical Power Supply Connections to Vehicular Equipment

(Negative Ground System, Grounded Chassis Shown]

7

ure 2 shows a typical example. The power supply
offers overload protection; therefore, any fuse in the
equipment’s power cable is not required during
testing. In fact, a convenient connection point may
be to the fuseholder. Normally, the equipment chas­sis should be grounded. Usually, the negative po-

larity of the equipment is common with the chassis

and a jumper may be connected between the

(* )

and

(-)

terminals of the power supply.

In those cases where the chassis is not common
with the negative polarity, connect a separate test
lead free from the

(

-h- )

terminal of the power supply

to the chassis of the equipment being serviced.

Figure 3 shows the proper interconnection between
the power supply and the equipment under test for
all possible situations.

8

POWER
SUPPLY

EQUIPMENT
BEING

POWERED

EQUPMENT

POWER

BEING

SUPPLY

POWERED

-F'

If there is any doubt that the chassis

may not be
common with the negative polarity, use a se­ground connection from the

(*l

terminal
equipment chassis. No damage can result
technique is used.

Set the power supply voltage to the specification

voltage for the equipment being serviced

(normally

the voltage value of a fully charged vehicle

battery).

Set the current limit to the maximum input

current

specification plus 5%.

If specification information

is unavailable, start with a moderate current

limit

and find the overload threshold. Increase the

cur-

rent limit 5% above threshold to prevent

overload

turn-off during testing.

Note that most solid

state

receivers have a much higher load current

with

strong audio output. Therefore, the threshold

should

EQUIPMENT

POWER

BEING
POWERED

POWER

EQUIPMENT
BEING

SUPPLY

Figure 3. Power Supply Interconnect Possibilities

POWER SUPPLY

#l

f

RECOMMENDED ONLY FOR

POWER SUPPLY

#2

Figure 4. TWO Power Supplies Connected in Parallel for 4 Amp Output

be determined with audio output: otherwise, the
overload circuit will be activated upon reception of

audio.

Some of the vehicular equipment listed may re-

quire more than 2 amperes of load current. This is
especially true

of transceivers during the trans­mitting mode and some tape players in the track
change

mode. If you have only occasional need to

service

such equipment, another power supply is

not

necessarily required.

A vehicular battery of the
correct voltage and of sufficient capacity will suffice.
During

testing, the transmitter does not normally
need to be keyed except for short periods. The bat­tery will provide adequate power for such testing.

The power supply can be used as a battery charger
to restore the battery to full charge, and all non-

transmit testing can be done using the power supply

as the dc power source.

Refer to Figure 4. Although it is Possible to obtain

up to 4 amperes load current from two power sup

POWER SUPPLY

MODULE BEING

SERVICED

Set CURRENT LIMIT

to

specification

for module being

serviced.

Figure 5.

Typical Power Supply

quired for bench testing modules. Figure 5 shows a

typical test set-up. Connect the

(+)

and

(-)

outputs

of the power supply to the (+) and

(-)

power ter­minals of the module. Identical power is sometimes
required at two or more terminals of a module. If

so, jumper together these terminals. An earth

ground may or may not be required. A test hook-up
diagram for

bench

testing the module should be
obtained. It should specify the operating voltage
and current limit. The current limit will typically be
lower than those previously described for battery
operated and vehicular equipment, since only a
single module is being powered.

Module testing is more likely to require two sep­arate dc voltages simultaneously. Refer to the next
paragraph for information.

USING TWO POWER SUPPLIES
FOR TWO OUTPUT VOLTAGES

When two separate dc voltages are

required

Set VOLTAGE to

specification for
module being ser­viced.

plies connected in parallel, it is not recommended

except for use by highly experienced personnel.
The power supplies should not be connected directly
in parallel, but should be isolated by very low re­sistance so that balance is not so critical. Even with
this technique, the power supplies must be well
balanced or the unit carrying the heavier load will
overload and turn off, which, in turn, will cause the
other Power supply to overload and turn off. It is
very difficult to bring the power supply output of
both units up to operating voltage without disturb­ing the balance. One method to achieve balance is

to use an external switching arrangement which
allows selection of the load or a dummy load. The
dummy

load should be selected to draw approx-

imately 1

ampere at the operating voltage of the

main load:

½

ampere from each power supply. The

Power

supplies

can be accurately balanced into the

dummy

load without fear of overload, then switched

to the main load.
SERVICING PLUG-IN MODULES

Equipment containing plug-in modules is often

repaired

by replacing a malfunctioning module.

then servicing the defective module on the bench.
A dc Power source such as this power supply is

re-

Connection to Module For Bench Testing

simultaneously for testing equipment, two power
supplies may be used. Set the voltage and current
limit for each power supply independently as re­quired by each circuit.

Only the circuit reference

point must be common between the two supplies.

Figure 6 shows some typical examples of proper
power supply connections when using two units.
Take extra precaution to prevent reverse polarity

connections in’ such situations. The numerous con­nections can become confusing. Additional colors
for the test leads will be helpful. The power sup

plies are protected from reverse polarity damage

from an external voltage source (such as the other

power supply).

TWO POWER SUPPLIES IN SERIES

FOR O-100 VOLT OUTPUT

The power supplies may be connected in series
for output voltages over 50 volts at 0 to 2 amperes.
Figure 7 shows the correct connections. Set the
current limit for both supplies at the same value and
equalize the voltage between the two units. Since
both units are connected in series, an overload in
either unit will shut down the output from both

sup-

plies, The power supplies are built to permit stack­ing when two units are used.

9

EQUIPMENT

BEING

POWERED

NO. 2 (3

V)

POWER
NO. 2

POWER

NO. 2

POWER
NO. 1

POWER
NO. 2

SUPPLY

(15 V)

SUPPLY

(10 V)

Figure 6. Using Two Power Supplies for Two Output Voltages (Typical Examples1

USING

THE POWER SUPPLY

AS A BATTERY CHARGER

The power supply can be used as a battery
charger to restore the charge in rechargeable bat­teries such as lead-acid, nickel-cadmium and some
alkaline types. Refer to the battery manufacturer’s
charging specifications for proper voltage and cur­rent settings. Charging information is often printed
on the batteries. For batteries that specify maximum

charge currents of less than 2 amperes, set the cur­rent limit to the specified value. For batteries with
higher charge current capacities, set the current

limit to maximum. The charging current of a bat-

tery is highest when the charger (power supply) is

initially connected.

As a result, current overload
can occur before voltage is brought up to specified
charging voltage. If this happens, reduce the power

supply voltage slightly so the power supply does

not shut down. After a period of time, increase the
voltage until the full charge value can be obtained
without shutdown.

OTHER SERVICING APPLICATIONS

The instrument can be used as

a bias supply to

test the effects of varying the dc bias, such as the
AGC bias in a television receiver. Typically, the
equipment being tested contains its own power sup
ply and operates from ac power. DC voltages are
present in the circuits.

The power supply is floated
from an appropriate point in the circuit, such as the
emitter of a transistor. The power supply output is
then

applied

to another point, such as the base of
that transistor. Varying the power supply voltage
then varies the dc bias on that stage,

and

the effects

POWER SUPPLY

#l

POWER

SUPPLY #2

Figure 7. Two Power Supplies in Series

for Cl-100 Volt Output

may be noted.

A series limiting resistor is often

used to protect circuits from overdissipation.
ELECTRONICS MANUFACTURING

In electronics manufacturing, the power supply is
most often used as a dc power source to test
completed units for proper operation and compli­ance with specifications.

The

instrument could also
be used in incoming inspection to test purchased
equipments or subassemblies. The use of the power
supply for testing complete units is very similar to
that previously described for servicing battery op

erated

and vehicular equipment, while its use for
testing subassemblies is very similar to that de­scribed for servicing modules.

This power supply is particularly well suited for
manufacturing. applications because of its ease of
operation and the speed at which it will accomplish
its

job, in

addition to its other features. When load
current or total power dissipation are among the
main characteristics to be measured, the total load
current

and

voltage are instantly displayed on the

two meters.

The current limit can be adjusted so

that all units which do not meet the load current

specification will cause the overload to trip, and

the unit can be rejected.
ELECTRONICS

DESIGN ENGINEERING

The technician or engineer working in an

engi-

neering laboratory requires a power supply to

power prototype and experimental circuits. This
power supply is ideal because it monitors both cur­rent and voltage simultaneously, limits current to
protect the circuit, is adjustable over such a wide
range, and has excellent regulation and very low
ripple.

Use of the instrument in an engineering laboratory
is very similar to that previously described for serv­icing electronics equipment and modules, except

that lower currents may be prevalent when power­ing single stage experimental circuits. The current
limiting feature is very valuable in this application
because it protects the unproven circuit from
damage.

ELECTRONICS EDUCATION

The student in an electronics school may use the

power supply for powering equipment and circuits
as previously described for all other applications.

In addition, the power supply will be used in the
laboratory classroom to conduct experiments in fun­damental electronics. In learning

Ohm's

law, for

example, the relationships of resistance, current and
voltage are vividly demonstrated by the use of the
power supply. Being able to observe both the cur­rent and voltage meters simultaneously is a great
aid in such experiments. Figure 8 shows typical
examples of the types of experiments and exercises

that may be conducted.

!

POWER SUPPLY

OBSERVE

OHMS

LAW

BASIC VOLTAGE DIVIDER

R1

BASIC CURRENT DIVIDER

*xa

x1+12'11N

POWER SUPPLY

SERVE

STIC

OF DIODE

MEASURE VDI &

I

VARY

EIN

CHARACTERISTIC

OF

ZENER

DIODE

xi--~$~;:-~I

Rl

Figure

8.

Typical Laboratory Classroom Experiments Using The Power Supply

11

CIRCUU

IT DESCRIPTION

GENERAL

The power supply converts a 117 VAC input to a
highly regulated and filtered dc output that is fully
adjustable from 0 to 50 volts and 0 to 2 amperes.
The circuits that accomplish this action may be
divided into five main groups as follows:

-Unregulated B+ Source. Converts the ac input

into a raw, unregulated dc voltage.

_V+

and V- Source.

Converts the ac input to

+15

VDC (V+) and -15 VDC

(V-)

for powering
active elements ICI and IC2 in the control circuits
and control sensing circuits group.

-Control Circuits.

Controls the unregulated B+
source to provide a highly regulated B+ output
that is adjustable from 0 to 50 volts.

-Current

Sensing Circuits. Establishes the current

limit, senses the load current, and activates

an
overload detector that shuts down the power
supply if the current limit is exceeded.

-Metering. Monitors the output voltage and
current.

Refer to Figure 9, the functional diagram, and to
the schematic diagram. Circuit descriptions make
constant reference to these diagrams.

NOTE
The voltages in the following circuit de­scriptions, and on the diagrams, are meas­ured with respect to the regulated B+
output (the + terminal). Note that this
point is floating independent of the chassis
of the power supply.

UNREGULATED B+ SOURCE

The unregulated B+ source circuit converts the

117 volt ac input to a raw, unregulated B+ output.

Later,

in the control circuits, the unregulated B+ is

converted into the regulated B+ output of the power
supply.

The unregulated B+ output level is

pre-regulated
in coarse steps. As the LEVEL control is rotated
clockwise from zero to maximum, the unregulated
B+ voltage changes from its lowest to its

highest

value in four steps.

This minimizes the

difference

between the unregulated B+ and the regulated B+
output, which always keeps power dissipation

with-

in safe limits.

The main components which make up

this circuit

are power transformer

Tl,

pre-regulator switch

as-

sembly S5, bridge rectifier

BRl,

and filter capacitor

C8.

The ac input is applied to the unregulated

B+

circuit through on-off switch S4 (which is

part

of the

LEVEL control), across neon POWER lamp

NE1

(which glows continuously as a pilot lamp to

show

that power is on), to power transformer

Tl.

Power

transformer

Tl

has four taps in its

main

power out­put winding. At the lowest voltage setting, only the
low voltage portion of the

transformer

is connected
into the rectifier (this is the condition shown on the
schematic diagram). As the LEVEL control is rotated
clockwise, cams operate microswitches

S5-C,

then

S5-B,

and finally

S5-A.

Each cam-operated

micro­switch selects another tap on the secondary of the
power transformer and sequentially steps the rec­tifier input voltage to a higher value.

Bridge rectifier BRl converts the ac power to full
wave dc, which is filtered by C8. The unregulated
B+ output at C8 is regulated and filtered by the
control circuits.

V+ AND V- SOURCE

The V+ and V- source is a completely separate

power source for powering comparator

IC1.

and

voltage reference and error amplifier

IC2.

These

circuits must be free from the extreme voltage

var-

iations found in the other power source circuits.

Figure 9. Power Supply Functional Diagram

12

The control Power winding of

Tl.

diodes D9 and

DlO,

and filter capacitors Cl0 and

C11

form the

V+
and V- voltage source. These power source Cir­cuits provide

+

15 and -15 volts respectively. Both

the

V+

and

V-

voltages float with respect to the
regulated output, and are also independent of the
variable unregulated B+ voltage.

CONTROL CIRCUITS

The control circuits convert the unregulated B+

voltage

into

the regulated B+ voltage. The control

circuits establish the reguiated B+ level in

response

to the

setting

of LEVEL control R27. When R27 is

set for

O

volts, the following circuit conditions

exist:

__Voltage

reference IC2 provides a stable +7 V

reference at

IC2-6.

_The +7 V reference is divided across R13 and

Rl4 to

place

+3.5

V on the inverting input (pin

4)

of

error amplifier IC2.

_The regulated B- output voltage is

0

V.

_The

+7

V reference is divided across current

path

I,.

which consists of

R15,

R27 (Approx­imately 0 ohms at this time), R37 and R34. This
places approximately

+3.5

volts on the

non-

inverting input (pin 5) of error amplifier IC2.

__Since

the inverting and non-inverting inputs

to

IC2

are equal, no output is developed at

IC2-9.

_No

drive is applied to series pass regulator

Q1,

Q2 and the output remains at zero volts.

When LEVEL control Fi27 is increased to a higher

voltage level, the following circuit action

occurs:

__The

resistance of R27 is added to the voltage

divider network, decreasing current I,.

__The

voltage at

IC2-5

increased (less drop across

R15), and error amplifier IC2 produces an out-

put which biases regulator

Ql, Q2

into oper-

ation.

__The

regulator allows some of the unregulated

B+

to pass to the output terminals and the out-

put voltage rises.

-As

the output voltage rises, the B- becomes

more negative.

-Current

Jr

increases as B- becomes more nega-

tive,

and the voltage at

IC2-5

decreases until

balance is achieved.

When LEVEL control R27 is decreased, the oppo-

site action occurs. Once

R27

is set and balance is
achieved, any load current changes that tend to
change the

output

voltage are sensed and corrected.

CURRENT SENSING CIRCUITS

The major components in the current sensing cir-

cui

t

s are comparator

IC1.

overload switch

SCRl,
and current sensing resistors R1 thru R4. These
circuits monitor the load current and shut down the

power supply

if the preset current limit is exceeded.

First, let us examine the current sensing resistors

R1

thru R4.

These precision, low value resistors are

in

series with the

output

load current. The values

are

chosen so that the maximum current for a

chosen

range Produces exactly 1 volt drop

across

the

resistor (for example, if the 2A range is

selected

2 amps

through resistor R4 develops exactly

1

volt).

The voltage developed across the current
sensing resistor is applied as the non-inverting input
(pin 2) to comparator ICI.

The inverting input at pin 3 of comparator

ICl

is
a 0 to 1 volt dc potential selected by the SET CUR­RENT LIMIT control R8.

Whenever the output load current produces a
voltage drop across the selected current sensing
resistor

(R1

thru R4) that is greater than the preset

voltage on the inverting input of

IC1,

a Positive out-

put voltage of approximately 1 volt appears at the

output (pin 7) of comparator

ICl.

This voltage

drives the gate of overload switch

SCR1

and turns

it on. Overload switch

SCRl

grounds pin 10 of error
amplifier IC2, which inhibits its operation regardless
of all other inputs and shuts down the power supply.

SCR1

also provides the ground path which allows
the OVERLOAD lamp to light. Set/reset switch S3
opens the voltage path to SCRI to reset it to an off
condition.

The STBY-DC ON switch

(S6)

is also connected to

pin

10

of error amplifier IC2. In the STBY position,

this switch grounds

IC2-10

and inhibits its operation,’

thus disabling the power supply output.
METERING

Voltmeter Ml is connected directly across the out­put terminals to measure output voltage. Series
resistors, as selected by METER range switch S2,
calibrate the meter to read 0-25V or 0-5OV. A me­chanical interlock prevents the LEVEL control from
being increased above approximately 25 volts when
S2 is in the 0-25V range.

Current meter M2 is actually a voltmeter that is

calibrated to accurately measure output load cur-

rent. The meter measures the voltage that is de
veloped across the current sensing resistor, which
is exactly 1 volt for a full scale meter reading.
When setting the current limit, switch S3 is actuated,
which connects the current meter directly across the
SET CURRENT LIMIT control R8. This control se-

lects a voltage from 0 to

lV,

which very accurately

corresponds to the current limit value read on the

meter.

MAINTENANCE AND CALIBRATION

WARNING

-

THE FOLLOWING INSTRUCTIONS ARE FOR USE BY
QUALIFIED PERSONNEL ONLY. TO AVOID ELECTRICAL SHOCK, DO NOT
PERFORM ANY SERVICING OTHER THAN THAT CONTAINED IN THE OPER­ATING INSTRUCTIONS UNLESS YOU ARE QUALIFIED TO DO SO.

This power supply is built to provide long,
trouble-free service and does not require periodic
maintenance. If the unit malfunctions, use conven­tional troubleshooting techniques, such as voltage
and resistors checks, to isolate the defective com­ponent. If electrical components are replaced, the
unit should be recalibrated.

CALIBRATION

To gain access to the calibration adjustments, re-

move the 3 screws at the rear of the top cover, then
lift the top cover at the rear and slide the front lip
of the cover from the retaining bosses on the front
panel. Refer to Figure

10

for locations of calibration

adjustments.
MAX OUTPUT ADJ

(R24)

1. Connect an accurate, calibrated voltmeter to the
output terminals of the power supply.

2. Set the LEVEL control of the power supply to
maximum.

3. Adjust the MAX OUTPUT ADJ potentiometer

(R24)

for exactly 50.5 volts on the external volt-

meter.

25V CAL

(R33)

Connect an accurate, calibrated voltmeter to the

output terminals of the power supply.

Set the METER RANGE switch of the power sup­ply to the 25V position.

Adjust the LEVEL control of the power supply for

exactly 20 volts on the external voltmeter.

Adjust 25V CAL potentiometer

(R33)

for exactly

20 volts on the voltmeter of the power supply.

50 VOLT

25 VOLT

CURRENT

5OV

CAL

(R30)

1.

2.

3.

4.

Connect an accurate, calibrated voltmeter to the

output terminals of the power supply.
Set the METER RANGE switch of the power

sup-

ply to the

5OV

position,

Adjust the LEVEL control of the power supply for
exactly 50 volts on the external voltmeter.

Adjust

5OV

CAL potentiometer

(R30)

for exactly

50

volts on

the voltmeter of the power supply.

CURRENT

METER CAL (R-29)

1. Connect an accurate, calibrated ammeter ca­pable of 2A in series with an appropriate load

(1 ohm, 4 watts) to the output terminals of the

power supply.

2. Adjust the LEVEL control of the power supply

for exactly 2A on the external ammeter.

3. Adjust CURRENT METER CAL potentiometer

(R29)

for exactly 2A on the current meter of the

power supply.

INTERNAL CURRENT LIMIT ADJ. (R-21)

1. Turn SET CURRENT LIMIT (3) to full C.W.

2. Adjust R-21 to full scale when pressing the set/

reset button (4).

FUSE REPLACEMENT

If these is no power supply output and the

POWER lamp does not light, check fuse

Fl.

The

fuse

Fl

is located inside the cabinet, which is made

accessible by removing the 3 screws at the rear of

the top cover, then lifting the top cover at the rear
to slide the front lip of the cover from the retaining

bosses on the front panel.

Fuse

Fl

is soldered to a terminal strip at the right

of the main power transformer. Figure 10 shows the

location of the fuse.

INTERNAL CURRENT LIMIT ADJ

\

-ERChL

14

Figure

10.

Location of Calibration Adjustments and Fuses